Sorry this happened to you, Fidelia. It sounds like you all are trying to handle it well. It is very hard when it is new and there is little social context to go on. We are brought up in a world where the rules of monogamy are pretty much understood by most people. But polyamory is a learn as you go process.
It is good that your husband was honest with you about what he felt. It may be easier to liken it to something not so emotional. For example, my wife asked me to join her by the pool. I told her that I would be down ina minute since I was watching some funny videos on the web. Next thing I know, she is back in the house in her regular clothes. So I asked her when she was going to get her bathing suit on so I could join her outside. It turns out that I had been goofing off for about half an hour and she had finished swimming.
Sometimes we lose track of time. It doesn't mean that the other person is unimportant. It probably means that something new was happening that was overloading the normal thinking process. I think there are lessons for everyone in this. They need to realize how easy it is to loose track of time and need to keep you in mind. You should let them know that you are waiting for them before it becomes an annoyance to you.
A lot of getting polyamory to work is to keep all communication open. Tell Star when you are feeling jealous and encourage her to do the same. Let your husband know he can tell you if he is feeling jealous. of you and Star. Communicate your desires but always be open to negotiations and don't see any rule was a "forever" rule.
If it happens again, just go out there before you get annoyed and join them where they are. Or suggest you are waiting.
i wish you well.